1. Field of the Invention
The present invention relates to high-frequency signal amplification devices and to methods for manufacturing the same. The present invention particularly suitable to devices for amplifying signals in high-frequency bands (above 800 MHz, especially 800 MHz to 2 GHz).
2. Description of the Related Art
Semiconductor elements for amplification of high-frequency signals (high-frequency amplifiers) used in mobile communication, for example in cell phones, often are mounted on dielectric multilayer substrates with multilayer interconnections, in order to achieve smaller size and lighter weight. Also, to achieve smaller size, recess portions (cavities) are formed on a portion of the surface of the dielectric multilayer substrates, and semiconductor elements are mounted in such cavities.
FIG. 14, FIG. 15 (cross-sectional view along the line Vxe2x80x94V in FIG. 14), and FIG. 16 (cross-sectional view along the line VIxe2x80x94VI in FIG. 14) show an example of a conventional high-frequency signal amplification device, in which a semiconductor element is mounted in a cavity. This high-frequency signal amplifier uses a dielectric multilayer substrate 101 with four dielectric layers 111, 112, 113, and 114. When layering the dielectric layers, the dielectric layers are provided with a hole, thus forming a cavity 104. Metal conductors 102, 103 (131, 132 . . . 137 . . . ) formed on the dielectric layers 112 and 113 are exposed at the cavity 104. In this high-frequency signal amplification device, a semiconductor element 105 is die-bonded to the metal conductor 102, and wire-bonded with metal wires 106 to the metal conductors 131, 132 . . . 137 . . . , which are formed at a higher position (closer to the surface) than the metal conductor 102.
However, when the semiconductor element 105 is made smaller, and thus the spacing between the metal conductors 131, 132 . . . 137 . . . is made narrower, in order respond for miniaturization, the problem of so-called insufficient isolation is aggravated. With insufficient isolation, capacitive coupling between the metal conductors tends to occur in the high-frequency band, due to the shrinking distance Lxe2x80x2 between the metal conductors (see FIG. 15). Thus, insufficient isolation leads to instability of the operation of the element, and depending on the operating conditions, may lead to oscillations.
In order to eliminate insufficient isolation, JP H07-170090A suggests providing separation grooves between circuits in a dielectric substrate with a base metal on which a FET carrier is mounted. As shown in FIG. 17, a separation groove 201 is formed in a dielectric substrate 204, for example between an output circuit 202 and an interstage circuit 203 between stages of amplification with a plurality of FETs. When this separation groove is formed, the dielectric constant of air (which is 1) in the separation groove is smaller than the dielectric constant of the dielectric substrate, so that dielectric coupling due to electric fields between the circuits can be suppressed. The above-noted publication also discloses a method for forming the separation groove by die cutting together with an aperture accommodating the FET carrier before baking the dielectric substrate.
In order to mount the FETs on the carrier and place the carrier on the dielectric substrate of the device disclosed in JP H07-170090A, it is necessary to provide the carrier with die bonding regions, wire bonding pad regions, etc., and to provide the aperture portion of the substrate with a margin when placing the carrier. For this reason, this dielectric substrate is less suitable for miniaturization than the device using a dielectric multilayer substrate as shown in FIGS. 14 to 16. Also, since for manufacturing reasons it is necessary to provide a margin (Mxe2x80x2 in FIG. 17) between the edge of the circuits and the edge of the separation groove disclosed in JP H07-170090A, this margin becomes an obstacle to shortening the distance between the circuits. Considering the precision of the actual manufacturing steps, it is necessary to provide a margin Mxe2x80x2 of about 200 xcexcm. When this margin cannot be ensured, there is the danger that the width of the conductors is reduced by the separation groove, so that their impedance changes, which leads to a degradation of the high-frequency characteristics.
Consequently, when trying to apply the separation groove disclosed in JP H07-170090A to a high-frequency signal amplification device using the dielectric multilayer substrate shown in FIGS. 14 to 16, it is necessary to ensure a sufficient margin Mxe2x80x2, so that the spacing between the metal conductors becomes large, which runs counter to attempts to make the device smaller.
Thus, with conventional high-frequency signal amplification devices, it is difficult to make the device smaller and at the same time ensure isolation. Therefore, it is an object of the present invention to provide a high-frequency signal amplification device, in which insufficient isolation is compensated and which is made smaller, as well as a method for manufacturing the same.
In order to achieve this object, a high-frequency signal amplification device in accordance with the present invention includes:
a dielectric multilayer substrate including a plurality of dielectric layers;
a semiconductor element with high-frequency signal amplification function mounted on the dielectric multilayer substrate;
a plurality of metal conductors arranged between the plurality of dielectric layers and/or at a surface of the dielectric multilayer substrate; and
a metal surface that is arranged at a position lower than the plurality of metal conductors;
wherein the metal conductors are exposed at a portion of a first region of the surface of the dielectric multilayer substrate, and the metal surface is exposed from a remaining portion of the first region not including the region on which the plurality of metal conductors are arranged;
wherein the semiconductor element is mounted on the first region; and
wherein a high-frequency signal is input into the semiconductor element via at least one of the plurality of metal conductors, and an amplified high-frequency signal is output from the semiconductor element via at least another one of the plurality of metal conductors.
With this high-frequency signal amplification device of the present invention, dielectric material is removed from a first region arranged for mounting the semiconductor element, which does not include the region on which the plurality of metal conductors are arranged, so that the device can be made smaller and at the same time, insufficient isolation can be compensated.
In order to achieve the above-mentioned object, a method for manufacturing a high-frequency signal amplification device comprising a dielectric multilayer substrate including a plurality of dielectric layers, and a semiconductor element with high-frequency signal amplification function mounted on the dielectric multilayer substrate, includes the steps of:
preparing a dielectric multilayer substrate in which a plurality of metal conductors are formed on a surface of at least one of the plurality of dielectric layers, such that, in any range within a first region of a first surface of the dielectric multilayer substrate, proceeding from the surface of the dielectric multilayer substrate in a depth direction of the dielectric multilayer substrate, the plurality of metal conductors or a metal surface that is arranged at a position lower than the plurality of metal conductors is reached before reaching a second surface of the dielectric multilayer substrate;
removing, with an agent capable of acting in a direction substantially vertical to the surface of the dielectric multilayer substrate and removing dielectric materials more readily than metals, in the first region of the dielectric multilayer substrate, a dielectric layer in a depth direction from the first surface of the dielectric multilayer substrate until reaching the metal conductors or the metal surface, and exposing the metal conductors and the metal surface in the first region; and
mounting the semiconductor element in the first region, such that a high-frequency signal is input into the semiconductor element via at least one of the plurality of metal conductors, and an amplified high-frequency signal is output from the semiconductor element via at least another one of the plurality of metal conductors.
According to this method for manufacturing a high-frequency signal amplification device in accordance with the present invention, dielectric material is selectively removed with laser light, so that there is no need to provide a margin for manufacturing reasons, as when forming separation grooves. With this manufacturing method, a high-frequency signal amplification device can be provided in which dielectric layers, not including the region where the metal conductors are formed, are selectively removed.